The present invention is directed to bicycles and, more particularly, to a bicycle signal processing device that operates more reliably in the bicycling environment.
Many bicycle signal processing systems have been developed. A typical system often gathers and displays information related to bicycle speed, cadence, distance traveled and the like. Such systems usually include a magnet mounted to a wheel spoke, a magnet mounted to one of the pedal cranks, and magnet sensors mounted to the bicycle frame for sensing the passage of the magnets as the wheel and crank revolve. An electrical pulse is generated every time a magnet passes its associated sensor (e.g., once per wheel or crank revolution). The speed of the bicycle can be calculated based on the number of pulses received from the wheel sensor per unit of time and the circumference of the wheel. Similarly, the distance traveled can be calculated based on the number of pulses received over a length of time and the circumference of the wheel. The cadence can be calculated based on the number of pulses received from the crank sensor per unit of time. One or more switches ordinarily are provided for entering operating parameters (e.g., the wheel circumference), for selecting what information is displayed to the rider, and for starting and stopping various timers used for calculating the desired information.
More sophisticated systems have the ability to display information related to the state of the bicycle transmission. For example, some bicycles have a plurality of front sprockets that rotate with the pedal cranks, a plurality of rear sprockets that rotate with the rear wheel, and a chain that engages one of the front sprockets and one of the rear sprockets. A front derailleur is mounted to the bicycle frame for shifting the chain among the plurality of front sprockets, and a rear derailleur is mounted to the bicycle frame for shifting the chain among the plurality of rear sprockets. Manually operated switches or levers may control the front and rear derailleurs. Position sensors (e.g., potentiometers or contact sensors) are mounted to the switches or levers so that the front and rear sprockets currently engaged by the chain may be determined by the positions of the corresponding switches or levers. Such information may be displayed to the rider so that the rider may operate the transmission accordingly. Even more sophisticated systems use small electric motors to control the bicycle transmission. The motors may be controlled manually by the foregoing switches or levers, or automatically based on bicycle speed and/or cadence.
The switches, sensors and other electrical components of the signal processing system are often spaced apart from each other and are connected by wires. Not surprisingly, it is desirable to construct the system such that the components are easily installed and removed and to ensure that the electrical signals are reliably communicated from one component to another. To facilitate assembly and removal of the components, it is common to construct the signal processing system as a modular unit, wherein the individual components are connected to each other using detachable electrical connectors. However, when a bicycle is ridden in a wet environment, moisture may enter the connector and form a conductive path to other electrical components or to the frame, thus causing a short circuit or otherwise altering the signals communicated along the wires. The effect is particularly severe when the signals communicated along the wires are at high impedance. Because of the small amount of current associated with signals communicated at such high impedance, a very small amount of current flowing away from a signal wire can result in a large effect on the signal traveling through that wire, usually in the form of an unacceptably large change in signal voltage. As a result, waterproof connectors must be used to connect the components together, thus increasing the cost of the device.
Finally, because the number of components may be large, it is usually desirable to minimize the number of wires running along the bicycle. Such minimization of wiring not only decreases the cost of the device but also minimizes the number of connectors needed to connect the device together.